fix(manifest): update test

Well, this reminds us to refactor the testing suite... This currently is pretty
dangerous, since the scopes are mixed up and there is no proper isolation
between test blocks.

PSConfluencePublisher/Manifest.Tests.ps1

@@ -59,9 +59,9 @@ Describe 'Set-Manifest' `
                  Mock Set-Content {
                     Should -Invoke -CommandName 'Set-Content' -Exactly -Times 1
 
-                    $args[1] | Should -Be 'foobar.x'
+                    $Path | Should -Be 'foobar.x'
 
-                    $args[3] | Should -Be ($mockManifest | ConvertTo-JSON)
+                    $Value | Should -Be ($mockManifest | ConvertTo-JSON)
                  }
 
                  #mocking Get-Content, therefore file name can be bogus